A submarine canyon is a steep-sided valley cut into the seabed of the continental slope. Most are carved by turbidity currents, dense flows of sediment-laden water that run downslope, and some are as deep as large canyons on land.
Key takeaways
- Submarine canyons cut into the continental slope, the steep drop between the shelf and the deep ocean floor.
- Their main carver is the turbidity current, a dense flow of muddy water that runs downhill under water.
- Our list names 173 canyons, including Monterey Canyon, only 3 km from United States of America at its listed point.
- Ice Age sea levels were never low enough for rivers to have carved the deepest canyons.
How a submarine canyon works
A submarine canyon is a steep-sided valley cut into the seabed of the continental slope [1]. The slope is the steep part of the continental margin, between the shallow shelf and the deep ocean floor, and the canyons run down it like gullies down a hillside. Their walls are often nearly vertical, and some rise up to 5 km from floor to rim [1].
The main carving process is the turbidity current. This is a dense flow of water loaded with sediment that runs downslope along the seabed, because it is heavier than the water around it, and it scours the canyon floor as it goes [1]. Underwater landslides and slumping also add to the work, and earthquakes can set them off [1].
Many canyons lie more than 2 km below sea level [1]. Wikipedia gives Avilés Canyon, off Spain, as reaching about 4,700 m, and Nazaré Canyon, off Portugal, about 5,000 m [1]. Both are in our list: Avilés Canyon and Nazaré Canyon.
An example from our data
Our list has 173 named canyons. Monterey Canyon is the one most people know. Its listed point is 3 km from United States of America, so the canyon reaches in close to the coast.
Congo Canyon lies 58 km from Angola, and Nazaré Canyon lies 46 km from Portugal. Hudson Canyon is 124 km from the United States of America. Because the depth in a canyon changes so much along its length, one depth figure does not describe it well. The feature pages explain which cell the grid figure comes from.
The drain slider shows how small an Ice Age fall in sea level is next to a canyon. Lowering the sea by 120 m, as the 120 m step does in a simple bathtub model, exposes 21.7 million km² of seabed, and it still leaves the deep canyons far below the surface. The model lowers the sea by the same amount everywhere and ignores ice sheets, so treat it as an illustration only. The homepage has more on what the Ice Age land bridges looked like.
The thing people get wrong
Many people were taught that submarine canyons are old river valleys, drowned when the sea rose after the Ice Age. That theory gets part of the picture: a lower sea does let rivers run further out across the shelf. But it cannot explain canyons mapped at depths near 3,000 m, since the sea never fell that far [1]. Turbidity currents are now seen as the main carver, with landslides adding to it [1].
A second mistake is to think a canyon always has one simple cause. Some deep canyons may also form when an enclosed sea dries up and rivers cut deeper into the exposed basin, as in the Messinian salinity crisis in the Mediterranean [1].
Submarine canyon vs ocean trench
| Submarine canyon | Ocean trench | |
|---|---|---|
| Where | Cut into the continental slope | Where one plate sinks under another |
| Cause | Turbidity currents and landslides [1] | Plate subduction |
| Main direction | Runs down the slope, from shelf to deep sea | Runs along the plate boundary |
Frequently asked questions
How are submarine canyons made?
Mainly by turbidity currents, dense flows of sediment-laden water running down the slope. Underwater landslides and slumping also contribute, and earthquakes can trigger them.
Were submarine canyons carved by rivers in the Ice Age?
Not the deepest ones. An early theory said so, but it does not explain canyons mapped around 3,000 m down, because sea levels never fell that far.
Sources
- Submarine canyon, Wikipedia.
- What is the continental margin?, NOAA Ocean Service.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).